Cephalexin: What It Is, How It Works, and What You Need to Know

When you hear cephalexin, a first-generation cephalosporin antibiotic used to treat common bacterial infections. Also known as Keflex, it’s one of the most prescribed antibiotics for skin, bone, and respiratory infections. Unlike some newer drugs, cephalexin doesn’t require special monitoring, but that doesn’t mean it’s harmless. It works by breaking down the cell walls of bacteria—simple, direct, and effective against many strains like staph and strep. But it won’t touch viruses, and using it for the wrong infection is not just useless—it can make future treatments harder.

People often ask if cephalexin is the same as amoxicillin, a penicillin-class antibiotic commonly used for ear infections and sinusitis. They’re both broad-spectrum, but they work differently. Amoxicillin is better for some respiratory bugs, while cephalexin shines in skin infections like cellulitis. If you’re allergic to penicillin, cephalexin is often the next step—but not always safe. About 10% of penicillin-allergic people react to cephalosporins too. That’s why doctors check your history before prescribing. It’s also not the first choice for urinary tract infections anymore; nitrofurantoin or trimethoprim are usually preferred. But for simple infections in healthy adults, cephalexin still holds its ground.

Side effects are usually mild—stomach upset, diarrhea, or a rash—but if you get severe watery diarrhea or abdominal cramps, stop taking it and call your doctor. That could be C. diff, a dangerous infection triggered by antibiotics wiping out good gut bacteria. And yes, it can interact with other meds. If you’re on probenecid for gout, cephalexin sticks around longer in your body, which might raise your risk of side effects. It’s also worth noting that cephalexin is often sold as a generic antibiotic, a lower-cost version of brand-name drugs with the same active ingredient and effectiveness. That’s why you see it everywhere: it’s cheap, stable, and works when it’s supposed to.

There’s no magic here. Cephalexin isn’t a miracle drug, and it’s not meant for every infection. But when used right—correct dose, full course, proper diagnosis—it’s reliable. You’ll find posts here that dig into how it stacks up against other antibiotics, what to do if it doesn’t work, and why some people end up with allergic reactions after taking it for years without issue. You’ll also see real-world comparisons with drugs like amoxicillin, clarithromycin, and doxycycline, so you understand when cephalexin is the best pick—and when it’s not.